1. Field of the Invention
The present invention relates to a base unit, and more specifically to a base unit for use in a storage disk drive apparatus, a spindle motor including the base unit, and a storage disk drive apparatus including the spindle motor.
2. Description of the Related Art
JP-A 2006-40423 describes a known hard disk drive apparatus. This known hard disk drive apparatus includes a magnetic disk, a head arranged to write and read data to or from the magnetic disk, and a case arranged to contain the magnetic disk and a driving portion arranged to drive the head.
The magnetic disk includes a plurality of concentric tracks. Each of the tracks includes data areas in which data is stored, and servo areas in which servo data is stored. Data is written to or read from the magnetic disk while the position of the magnetic head is identified using the servo data with the magnetic disk being rotated.
Regarding hard disk drive apparatuses in recent years, there has been a push towards smaller track intervals and hence greater track densities in order to achieve higher capacities. There is a need for the servo data, which is used to control positioning of the head, to be recorded with higher precision in order to achieve smaller track intervals.
Accordingly, JP-A 2006-40423 discloses a technique of trapping a gas (e.g., helium, hydrogen, or the like) having a smaller density than that of air in the case of a hard disk drive. This technique enables the servo data to be recorded with higher precision while reducing oscillation, irregular rotation, etc., of the magnetic disk, that is, while reducing so-called “flutter” of the magnetic disk.
When a user uses the hard disk drive apparatus with helium or the like trapped in the case thereof, the rotational resistance of the magnetic disk is reduced because of reduced flutter of the magnetic disk, which makes it possible to reduce a required electrical current value of a motor used to rotate the magnetic disk.
In a spindle motor installed in the hard disk drive apparatus as described above, lead wires drawn from coils of different phases of the motor are intertwined together. Common wires intertwined together into a single stranded wire are passed through a through hole defined in the case and drawn out of a base. The common wires drawn out of the base are connected to a circuit board through a solder below the through hole. The through hole is sealed with the solder, an adhesive on the circuit board, and so on.
The structure as described above, however, may not be able to prevent the gas such as helium or the like inside the case from leaking out of the hard disk drive apparatus, leading to deterioration in the purity of the gas trapped in the case of the hard disk drive over the life of the hard disk drive apparatus.